l8> 



^^^ Carbohydrates 



M onosaccharides 



The carbon reduction cycle (Figure 2) includes as in- 

 termediate compounds the following sugar phosphates: 3- 

 phosphoglyceraldehyde, dihydroxyacetone phosphate, fruc- 

 tose- 1,6-diphosphate, fructose-6-phosphate, erythrose-4-phos- 

 phate, sedoheptulose-l,7-diphosphate, sedoheptulose-7-phos- 

 phate, xylulose-5-phosphate, ribulose-5-phosphate, ribose-5- 

 phosphate, and ribulose-l,5-diphosphate. Besides these com- 

 pounds, glucose phosphates are found to be very rapidly 

 labeled in all plants in which we have studied the photosyn- 

 thesis of carbon compounds from C^^02. When characterized, 

 both glucose-6-phosphate and glucose- 1 -phosphate have been 

 found. Other sugars found to be labeled somewhat more 

 slowly in these experiments and identified as the free sugars 

 following hydrolysis of the sugar monophosphate area include 

 mannose and galactose. 



In virtually all the studies of the labeled products of the 

 photosynthesis of carbon compounds from C^'*02 there has 

 been found a striking absence of unphosphorylated mono- 

 saccharides (14). This is hardly surprising, since photosyn- 



49 



